A nuclear power plant control system that controls a nuclear power plant includes a plurality of independently operating systems to achieve high reliability (for example, see Patent Literature 1). An example of a configuration of the nuclear power plant control system including a plurality of systems will be described with reference to FIGS. 5 and 6.
FIG. 5 is a diagram illustrating an example of a configuration of a conventional nuclear power plant control system. A nuclear power plant control system 1 illustrated in FIG. 5 is a control system that controls a nuclear reactor trip, and includes a duplex channel and a duplex train. Herein, a channel is a system that detects a phenomenon occurring in a nuclear power plant, and a train is a system that performs a logical operation based on a detection result of the channel.
In the nuclear power plant control system 1, a detection unit 10a included in a channel I includes a sensor that detects a specific phenomenon (for example, a rise in pressure in a particular part and the like) occurring in the nuclear power plant, and a threshold operation unit that performs a threshold operation of a detected value of the sensor. When a detected value of the sensor exceeds a threshold, the detection unit 10a outputs a signal that indicates an occurrence of a specific phenomenon to an input unit 21a included in a train A.
A detection unit 10b included in a channel II includes a sensor and a threshold operation unit similar to those of the detection unit 10a, and outputs a signal that indicates an occurrence of a specific phenomenon to an input unit 21b included in a train B when a detected value of the sensor exceeds a threshold.
A trip control device 20 including the input unit 21a and the input unit 21b trips a nuclear reactor when a signal is input to at least one of the input unit 21a and the input unit 21b. By such a configuration, the nuclear power plant control system 1 may maintain a function even when a malfunction occurs in a portion of the channel or the train.
FIG. 6 is a diagram illustrating an example of a configuration of a recent nuclear power plant control system. A nuclear power plant control system 2 illustrated in FIG. 6 is a control system that controls a nuclear reactor trip, and includes a quadruple channel of a channel I to a channel IV. A channel I includes a detection unit 30a and an input unit 41a. A channel II includes a detection unit 30b and an input unit 41b. A channel III includes a detection unit 30c and an input unit 41c. A channel IV includes a detection unit 30d and an input unit 41d. 
In the nuclear power plant control system 2, the respective detection units 30a to 30d include a sensor that detects a specific phenomenon occurring in a nuclear power plant, and a threshold operation unit that performs a threshold operation of a detected value of the sensor. When a detected value of the sensor exceeds a threshold, the detection units 30a to 30d output a signal that indicates an occurrence of a specific phenomenon to an input unit 41 included in the same channel.
A trip control device 40 including input units 41a to 41d trips a nuclear reactor when a signal is input to at least two of the input units 41a to 41d. By such a configuration, the nuclear power plant control system 2 may maintain a function even when a malfunction occurs in a portion of the channel.